In fluid blast equipment for industrial cleaning, high pressure fluid blast guns are supplied by a high pressure fluid blast pump. Such high pressure fluid blast guns are used for cleaning and removing unwanted deposits or coatings off various types of surfaces and for cleaning interior surfaces of tubes. High pressure fluid streams used in cleaning applications are provided with pressures in excess of 5,000 p.s.i. typically at pressures of 10,000 p.s.i. A fluid blast gun is typically provided with a high pressure nozzle. Water is generally used as the blasting medium. Frequently, for economic reasons, it is desired to connect more than one fluid blast gun to a single fluid blast pump. In this configuration each gun is operated independently either at extremely high fluid pressure or, when discharge of high pressure fluid is to be discontinued, at low pressure with the water flowing through a dump outlet in the blast gun's control valve.
Heretofore, a problem has arisen in a multiple blast gun configuration when one operator of one fluid blast gun has stopped blasting as other fluid blast gun operators continue. When one operator stops blasting, the fluid from his gun is dumped at low pressure from the gun's dump nozzle as described in detail in U.S. Pat. No. 4,602,740. When dumping from the gun's dump nozzle at low pressure occurs, fluid pressure in the system for the other guns becomes insufficient for blasting. Therefore, various attempts have been made to maintain blasting pressure at all fluid blasting guns while one gun is dumping at low pressure. These include complicated multi-operator style guns that incorporate an internal orifice with an internal valving means to stop the water flow to the gun's blast nozzle and divert it through the orifice, they also include separate control valves that incorporate internal orifices or require difficult field wrench adjustments to be made on them.
Examples of devices designed to maintain blasting pressure at all fluid blasting guns while one gun is dumping are the Goss Hydraulic Gun system, U.S. Pat. No. 3,802,628, and the Pacht Fluid Delivery system, U.S. Pat. No. 3,831,845. The Goss patent depicts a multi-operator gun that requires critical adjustments to be made to the internal valve actuating means and also an internal orifice to be installed in the gun that hydraulically matches the blasting nozzle or orifice in the gun. These types of guns are expensive, difficult to maintain and require the operator to have a number of internal orifices on hand that hydraulically match any blasting nozzles he may use in the field. The Pacht device provides a more convenient system of maintaining blasting pressure at all blasting guns because it is a device that is used in conjunction with the more commonly used single-operator dump style guns and it can be installed in the blasting system only when multi-gun blasting off of one blasting pump is desired. However, the Pacht system again requires the use of a specially sized orifice in its valve system member that is the hydraulic equivalent to the blasting nozzle or, in another version, it requires a difficult wrench adjustment to be made to the device's valve seat. This valve seat adjustment is difficult because the seat must be turned against full system pressure (10,000 p.s.i.) and this usually requires two adjusting personnel. Also, the seating configuration on the valve system and the corresponding valve seat on this device makes the field adjustment of the valve seat very sensitive and exacting. If the seat is adjusted too close to the valve stem a dangerous system overpressure condition can occur.
Still other prior art control valves that are designed to be used in conjunction with commonly used single operator dump style guns utilize an internal valving system to divert the high pressure water through an internal orifice when the operator's gun is dumping. These devices also require the internal orifice in the control valve, therefore, when the operator changes the size of his blast nozzle, he must also disassemble the control valve, install the correct internal orifice and reassemble the control valve. Frequently, because he often uses multiple-orifice nozzles such as those used for cleaning the internal surfaces of tubes, he does not know the correct size of the internal orifice required in the control valve and must arrive at its correct size on a trial and error basis. This means that he must depressurize the blasting system, change the orifice and repressurize the system several times before the correct internal orifice size is established. Beside being tedious and time consuming, this orifice changing dictates that the operator have many sizes of internal orifices on hand. As a rule, the process of changing and matching the internal orifice to the blast nozzle results in considerable loss of the operator's time and down-time of equipment. This translates to a loss of revenue to the equipment owner.
U.S. Pat. No. 4,602,740 describes a fluid blast control apparatus, including a valve cartridge assembly for use with a single operator fluid blast gun. The valve cartridge assembly according to U.S. Pat. No. 4,602,740 is not effectively employed to adjust the pressure drop across the system because the tapered portion at the end of the valve closure member approaches the valve seat too rapidly for the desired range of adjustment of throttling pressure. Moreover, the valve closure member described in U.S. Pat. No. 4,602,740 was not designed to throttle high pressure fluids but rather to operate in either a full-open or a full-closed position. U.S. Pat. No. 4,602,740 describes a valve cartridge assembly in which the valve closure member is in a fully open position when the fluid blast gun is dumping fluid and in a fully closed position when the fluid is diverted through the high pressure nozzle.
It would therefore be advantageous to control the fluid flow and pressure in a high pressure blasting system wherein multiple blast guns are connected to a common blast pump with a fully adjustable type of control valve that does not require the installation of internal orifices and that also could be used in conjunction with common single-operator style dump guns. It would be further advantageous if the adjustment of such a control valve be made easily and externally without requiring difficult and dangerous wrench adjustments. It would be further advantageous if the control valve was of simple construction and the critical wear parts such as the adjustable valve and seat were packaged in cartridge form to facilitate quick and easy repair of the control valve in the field.